The present disclosure relates to a developing device used in an image forming apparatus such as a printer, and relates particularly to a developing device adopting a two-component developer containing a carrier and toner, and an image forming apparatus including the same.
An image forming apparatus utilizing an electrophotographic method, such as a copy machine, a printer, or a facsimile, is configured so that an electrostatic latent image formed on an image bearing member (for example, a photosensitive drum or a transfer belt) is supplied with a developer and developed therewith to form a toner image on the image bearing member. As one of methods for performing the development, there is known a touch-down development method using a two-component developer containing toner that is a non-magnetic substance and a carrier that is a magnetic substance. In this case, a two-component developer layer (so-called magnetic brush layer) is borne on a magnetic roller, and toner is moved from the two-component developer layer onto a developing roller, and thus a toner layer is borne thereon. Moreover, toner is supplied from said toner layer to the image bearing member and used to visualize the electrostatic latent image.
In recent years, developing devices adopting the touch-down development method have advanced in terms of their operation speeds, and this has led to a demand for an improvement in their development performance. For example, there has been disclosed a technique for adjusting development performance by varying a duty ratio of an alternating current component of a development bias used at the time of a development operation. By this technique, part of toner on a developing roller, which has a poor flying characteristic, is favorably moved to an image bearing member.
The conventional technique, however, has presented a problem that, due to an increase in operation speed of such a developing device, toner is scattered when being delivered between a magnetic roller and a developing roller. Toner thus scattered is troublesome in that it gathers in a housing of the developing device and then adheres to a photosensitive drum or is spewed out through a gap in the housing into an image forming apparatus.
The present disclosure has been made to solve the above-described problem and has as its object to provide a developing device that prevents toner from being scattered when being delivered between a developing roller and a magnetic roller, and an image forming apparatus including the same.